Photoelectric cell



June 3, 1941. sgrrz JR 2,244,264

PHOTOELECTRIC CELL Filed Sept. 27, 1937 Patented June 3, 1941rno'roELEo'rmc cELL Louis J. Seitz, Jr., Elizabeth, N. J., assignor toWeston Electrical Instrument Corporation, Newark, N. L, a corporation ofNew Jersey Application September 27, 1937, Serial No. 166,026

' Claims.

This invention relates to photoelectric cells and more particularly tocells of the dry disk or barrier layer type.

This type of cell includes a layer of light-sensitive material between aback electrode and a light-transmitting outer or contact electrode. Nodifficulty is experienced in establishing a good electrical connectionbetween the back electrode and an external circuit but priorarrangements for providing a terminal connection to the outer electrodehave not been entirely satisfactory. The'current output of the cell toan external circuit will not remain constant during use when theterminal is held against a portion of the outer electrode (hereinaftertermed the cell contact area) under a relatively light pressure.-

It was found, however, that an increase in contact pressure resulted ormight result in several disturbing effects. Pressure between theterminal and the cell contact area tended to cause a decrease in theinternal resistance of the cell, thus altering the cell characteristics.The full effect of this resistance change was not always immediatelyevident, and it would frequently occur that the cell characteristicswould alter after the cell had been calibrated. A release of the contactpressure usually caused the internal resistance and dependent cellcharacteristics to alter again in a direction towards and possibly tothat of the original calibration.

A difliculty additional to that of the delayed change or drift in thecell characteristics was that the terminal had a tendency to dig into orthrough the cell contact area under the required contact pressure, thusshortening the electrical path through the cell as well as permanentlyisolating or destroying sections of the cell. This resulted in adecrease in the cell output as the damaged areas did not supply to theexternal circuit that part of the generated current that theyhad-originally contributed. g Variations in the size and shape ofresilient contact fingers on the terminal did not eliminate l thesedifllculties, and the soldering or welding of the terminals to the 'cellcontact area did not result in stable cell output during normal use.

An object of the present invention is to provide a barrier layer typephotoelectric cell having a terminal construction that eliminates theabove stated difiiculties and disadvantages. An object is to provide acell of the type stated in which the terminal construction provides acontact pressure adequate for stable output without producing a delayedchange or drift of the cell characteristics. A further object of theinvention is to provide a barrier layer type of cell including a softmetal bedding or pad between the terminal and the cell contact area.More specifically, an object is to provide a barrier layer photoelectriccell of the selenium type in which a bedding or pad of cadmium isarranged between the cell contact area and a terminal that engagesihesoft metal with a substantial contact pressure.

These and other objects and advantages of the invention will be apparentfrom the following specification when taken with the accompanyingdrawing in which:

Fig. 1 is a greatly enlarged and somewhat schematic perspective view,with parts in section, illustrating an embodiment of the invention;

Fig. 2 is a fragmentary enlarged sectionalview of a cell assemblyembodying the invention; and Fig. 3 is a front elevation, on a smallerscale, of the cell assembly of Fig. 2.

In Fig. 1 of the drawing, the barrier layer type I tion and/or to theminutely irregular surface of the layer 2. The lower terminal connectionmay be formed by an annulus I of copper, phosphor bronze or the like,which is held against the back electrode I when the cell is assembled ina 2 case or other mounting.

It has been the practice to form the other terminal as an annulus 5 ofphosphor bronze or other-resilient metal having a lug 6 for connectionto a terminal pin and a; plurality of resilient contact fingers 1 forengaging the outer electrode layer 3. An insulating ring 8 was usuallyarranged between the cell and the annulus 5, the

thickness of the insulation being such that the contact fingers ,l werepressed upon the electrode 3 when the cell and terminals were mounted ina case.

In accordance with the present invention, ,bedding or pads 9 of asoft'metal, such as cadmium or a low melting point bismuth-lead-tinalloy are arranged between the resilient contact fin gers 1 and theelectrode 3. The bedding metal flows or is deformed under the appliedpressure to conform to the irregularities in/ the upper surface of theelectrode 3, and thus establishes a uniform or approximately uniformpressure over the cell contact area.

istlc of the soldered terminal connections that were unsatisfactory. Thesoft metal appears to function as an electrical expansion joint whichprecludes substantial, change in the pressure upon the cell contact areawith changes in temperature, extent and conditions of use, and othervariables. i

The location of the cadmium layer between the outer electrode and thephosphor bronze terminal minimizes the possibility of damage to outerelectrode by electrolytic action in the event that moisture collectson-these contact areas. llhis protective action is due to the fact thatcadmium lies between the outer electrode metal and phosphor bronze inthe electromotive series.

In the mounted cell assembly of Figs. 2 and 3, the case is formed by theouter cap I and a base ll having a projecting annular shoulder 12 uponwhich the cell C is supported. A washer i3 is arranged between theshoulder i2 and the bottom terminal 5. The soft metal bedding comprisesan annulus 5' whose outer edge overlies the insulating ring 8 and whoseinner edge lies between the closely spaced narrow contact fingers I ofthe phosphor bronze terminal ring 5 and the surface of the electrode 3.The cover glass ing over portions of said outer electrode, a layer ofsoft metal between" each resilient contact 7 electrical connections tospaced areas of said outer electrode, pads of soft metal between saidfingers and said areas, and means maintaining said fingers in resilientengagement with said pads of soft material..

5. The invention as claimed in claim 4, wherein said pads consist ofcadmium.

6. In a photoelectric cell assembly, the combination with a barrierlayer type cell having a layer of light sensitive material between aback electrode and an outer light-transmitting electrode, said outerelectrode having peripheral portions thereof providing the cell contactarea for connection to an external circuit, of a terminal engaging theback electrode, a layer of soft metal at the periphery of the outerelectrode, a second terminal having spring contact fingers projectinginto engagement with the soft metal layer, and a casing enclosing saidcell and H rests upon the terminal ring 5' and the as-.

sembly is clamped in place by pressure applied to the cover glass by thelip of the cap ll) through a washer I5 when the case sections arethreaded into each other. Terminal pins [6 project from the wall of thecasing cap [0 and are connected by leads, not shown, to the terminalrings 4, 5', respectively.

I have found that a cadmium ring 9 appr-oximately 0.004 inch thickserves adequately to maintain the pressure relationships that areessential for stability of cell output. A bedding layer of cadmium willnot alloy with selenium at the temperatures usually encountered, andtherefore no secondary action is introduced to afiect the cell output.

It is to be'understood that the invention is: not limited to theparticular constructions herein described and that there is considerablelatitude in the design and construction of photoelectric cellsconforming to this invention.

I claim:

1. In a photoelectric cell assembly, a barrier 7 layer type cell havinga back electrode and an" outer electrode, and means for establishing a.circuit connectionto portions of the outerelectrode at the peripherythereof; said means including a layer of. soft metal overlying saidportions of the outer electrode, and a terminal having resilient contactfingers engaging said soft metal layer with a pressure sufficient todeform the same.

2. In a. photoelectric cell assembly, a barrier layer type cell havingan outer electrode, a terminal extending around the periphery of saidcell and having resilient contact fingers extendterminals, said casingincluding -means to retain said terminals in relative positions whichestablish a substantial pressure of said contact fingers upon said softmetal layer.

7. In a photoelectric cell assembly, the combination with a barrierlayer type cell having a layer of light sensitive material between aback electrode and an outer light-transmitting electrode, said outerelectrode having peripheral por-' tions thereof providing the cellcontact area for connection to an external circuit, of a terminalengaging the back electrode, a layer of soft metal at the periphery ofthe outer electrode, a second terminal having spring contact fingersprojecting into engagement with the soft metal layer, a base supportingsaid cell and terminals,

. and acap adjustable with respect to said base to press said terminalstowards each other to establish a substantial pressure of said contactfingers upon said soft metal layer, said base and cap comprising acasing enclosing said cell and terminals.

' 8. In a photoelectric cell assembly, a cell comprising a layer ofcrystalline selenium between a back electrode and an outer electrode, aterminal contacting the back electrode, a ring of insulating materialoverlying the periphery of the outer electrode, a ring of cadmiumoverlying-said insulating ring and an adjacent portion of the outerelectrode, and a terminal having an outer annulus portion overlying theouter portion of the cadmium ring and resilient contact fingers inresilient engagement with the portion of said cadmium ring that overliesthe outer electrode.

9. A photoelectric cell assembly as claimed in claim 8, in combinationwith a casing enclosing said cell and comprising means to force saidsecond terminal towards said cell, thereby to press said contact fingersupon said cadmium layer.

10. In a photoelectric cell assembly, the combination with a barrierlayer type cell including a layer of crystalline material between a backelectrode and an outer translucent electrode, a terminal havingresilient contact fingers, and means adjustable to press said resilientcontact fingers towards said outer electrode, or means to preventvariation of the cell characteristics with incidental variations in arelatively heavy contact 5 outer electrode.

pressure established at said contact flngersby a given adjustment ofsaid first means, said variation-preventing means comprising a thinsheet of soft metal between said contact fingers and said LOUIS J.SEITZ, JR.

CERTIFICATE OF CORRECTI ON Patent No. 2,?J4lh26h. June 5, 1911.1.

LOUIS J. SEITZ, JR.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows! Page 2,second'column, line 20, claim ii, for the word "material" rend --metal-;and that the said -Letters Patent should be read with this correctiontherein that the same may conform to the record of the case in thePatent Office.'

Signed and sealed this 8th day of July, A. D. 19in.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

